In the U.S., there were just 39 executions in nine states this year, a 10 percent drop from 2012, and only the second time in the past 19 years the number has fallen below 40, the Death Penalty Information Center reported earlier this month. Judges handed down more than 80 death sentences, nearly the lowest number since 1976, when the U.S. Supreme Court upheld the death penalty. In comparison, the number of sentences in 1996 was 315.

As the number of state-mandated killings has fallen, so has public support for them. A Gallup poll published this year shows that in 2013, support for capital punishment reached its lowest level in 40 years — down to 60 percent, compared with 80 percent in 1994. In addition, 52 percent of those surveyed said they believe the death penalty is used unfairly, down from 58 percent in 2010, and 60 percent in 2006.

"In a Boston Globe poll of city residents, a strong majority (57 percent) supported a sentence of life without parole for Dzhokhar Tsarnaev, the man accused of the Boston Marathon bombing," said the report by the Death Penalty Information Center. "Only 33 percent supported a death sentence if he were convicted."

Why the change of heart? A big part of it may have to do with the emergence of DNA testing, which has exonerated 18 death-row inmates since 1993, when Maryland prisoner Kirk Bloodsworth became the first condemned man to win freedom through the practice. The Innocence Project, an organization that tries to free the wrongly accused, explains:

These DNA exonerations are a window into the criminal justice system’s flaws: While DNA testing is an option in just a fraction of all criminal cases, the factors proven to cause wrongful convictions exist regardless of whether the case involves DNA. Specific to the death penalty, our work has shown that innocent people are sentenced to die. Of more than 300 people exonerated through post-conviction DNA testing, more than 25 percent were convicted of murder. [The Innocence Project]

At the same time, police have come under increased scrutiny for coaxing false confessions out of suspects. Advocates have started criticizing the Reid technique, a popular police interrogation method that involves refusing to accept a suspect's denials, claiming the existence of a file that contains evidence of the suspect's guilt, and otherwise coercing the suspect into confessing. "The interrogators refusal to listen to a subject's denials causes feelings of hopelessness, which are compounded by the fake file and by lies about the evidence," a psychologist explained in a recent New Yorker piece on the topic. "Confession opens something of an escape hatch, so it is only natural that some people choose it."

There are other factors as well. Support for the death penalty peaked in the 1990s when many major urban areas in America were still recovering from crime waves. Furthermore, awareness about the death penalty's flaws increased after reports emerged in 2009 that the Texas criminal system may have wrongly killed an innocent man, which if true would be the first such incident in modern U.S. history. And then-Supreme Court Justice John Paul Stevens in 2008 added to the debate when he declared that he personally thought the death penalty was unconstitutional.

Still, the U.S. remains in the top five when it comes to state executions, joined by such illustrious company as China, Iran, Iraq, and Saudi Arabia. As a a recent editorial by The New York Times notes, as more places ban capital punishment, it becomes more concentrated in certain parts of the country. "All 80 death sentences in 2013 came from only about two percent of counties in the entire country, and all 39 executions — more than half occurred in Texas and Florida — took place in about one percent of all counties," the Times says. "Eighty-five percent of all counties have not had a single execution in more than 45 years."

That's a big problem:

The argument is not that all of these people are innocent, or that they deserve to be released. Most would be justly imprisoned for most if not all of their life. But the death penalty as applied in America now — so thoroughly dependent on where the defendant lives and how much money he can spend on his defense — violates the constitutional guarantees of due process and equal protection, and no longer can overcome the Eighth Amendment’s ban on cruel and unusual punishments. [The New York Times]